Communication technology called DTN (Delay Tolerant Networking) is known (see, for example, NPLs 1 and 2). DTN is one of techniques of computer networking for obtaining a method for coping with technical problems under extreme environments or mobile environments under which continuous network connection is impossible. In DTN, for various network forwarding techniques, inter-nodes (for example, terminals) are routed by the store-and-forward system and asynchronously exchange messages having arbitrary lengths.
In general communication such as TCP/IP (Transmission Control Protocol/Internet Protocol) communication, communication between a transmission terminal and a reception terminal is performed only when end-to-end connectivity is established between these two terminals.
In contrast to this, in DTN, the end-to-end connectivity does not need to be always established between a transmission terminal and a reception terminal in transmitting data. In DTN, data is transmitted only up to a relay terminal in the middle having end-to-end connectivity with the transmission terminal. In DTN, the relay terminal has the function of accumulating data. When the relay terminal is connected to a terminal that holds no data accumulated in the relay terminal upon movement of the relay terminal or a change in network connection state, the relay terminal transmits data accumulated in itself to the terminal. Repeating such operations results in end-to-end information transmission over time even if the transmission terminal and the reception terminal have no end-to-end connectivity between them at the moment data is transmitted.